Complex Photon Mass in Spherically Curved Space-Time: Consistency with Experimental Bounds and Dispersion Phenomena

The photon is conventionally treated as a massless particle within Maxwell’s electromagnetism, special relativity, and quantum electrodynamics (QED). However, numerous theoretical proposals and experimental efforts have suggested the possibility of a non-zero photon mass. Observational limits from astrophysical phenomena such as gamma-ray bursts (GRBs) and fast radio bursts (FRBs), as well as laboratory measurements, constrain the photon mass to extremely small upper bounds. In addition, anomalous dispersion experiments in optical media have reported superluminal group velocities, which may be interpreted in terms of an effective imaginary photon mass. Motivated by these findings, we propose a framework in which the photon rest mass is expressed in a complex form, consisting of a real component (consistent with existing photon-mass limits) and an imaginary component (associated with dispersion and curvature effects). In this work, we study the emergence of complex photon mass in a spherically curved space-time background and discuss its implications for light propagation and the possible connection to dark sector physics. Our formulation provides a unifying perspective on photon mass, compatible with both astrophysical observations and laboratory experiments, while suggesting new directions for testing physics beyond the standard light-speed paradigm.